[feature request] extract a single file from EROFS filesystem

[Gao Xiang]

Hi Mingye,

On Mon, Jul 14, 2025 at 12:55:06AM +0800, Mingye Wang wrote:
> Hi all,
> 
> >Gao Xiang Thu, 09 Jan 2025 01:36:16 -0800
> >On 2025/1/9 02:14, Daniel Erez wrote:
> >>Would it be applicable to introduce an option for extracting a specific file
> >>from the image?
> >>I.e. something similar to the '-extract-file' option available in unsquashfs tool [2].
> >I will add this later.
> 
> I am seeing a need for a similar feature in making dracut's lsinitrd
> work... a little better. I should add two cents of my own.

dump.erofs already supports `--cat` command to dump a single file.

> 
> * In "unsquashfs" there's not only '-extract-file' for passing in a
> list of files, but also a possibility for a list of paths to be
> specified directly as arguments. This would appear outlandish on an
> fsck utility.

Can those be replaced as dump.erofs --cat?

> * When extracting single files it might be desirable to *not* verify
> and pretend-extract the other files.

`fsck.erofs` can be used to dump a subtree in the future (exclude file
pattern can be applied), fsck/dump/mkfs tools are more common for
generic filesystems.

Mimick Squashfs-specific is not EROFS will do since I do see `un`-prefix
is common and lack of (even defacto) standardization.

Thanks,
Gao Xiang